Contaminants which are deposited on products or parts in mills and are unlikely to come out or stains on clothes, tablewares or bathtubs in the home usually contain oily substances. The contaminants or stains containing the oily substances have been hitherto remove by means of detergents and water. Detergents, in turn, contain not less than 20% of surface active agents. The water obtained by removing oil stains with surface active agents is a kind of emulsion, whichever O/W emulsion or W/O emulsion, caused by the emulsifying action of the surface active agent.
At present, any provision has not been regulated with respect to the discharge of waste water from domestic life. Where waste water from mills is discharged to rivers or seas, emulsified water is prohibited from discharge. More particularly, only water after removal of oily substances therefrom has been permitted to be discharged to rivers or seas. Industrial waste water from a diversity of companies has to be one which is obtained by separating emulsified water into water and oil phases and removing the oil phase therefrom.
Prior art methods of separating emulsified water into water and oil phases include (1) a natural separation method using gravity, (2) a centrifugal separation method using centrifugal separators, (3) a filtration method using passage through a filtering machine under pressure, (4) a heating method comprising heating at 40.degree..about.60.degree. C. and separating in a heating condition, (5) a high voltage electric field method wherein a high voltage of about 10000 V is applied, and (6) a chemical treating method which makes use of chemicals capable of de-emulsifying the emulsion. According to any of these methods (1).about.(6), it takes much time before separation into water and oil phases or the equipment costs become very high. Thus, the prior art methods could not separate the an aqueous emulsion into oil and water phases at low costs within a short in a simple manner.
Washing water for products and parts in mills usually contain rust preventives. This is because ordinary water such as city or well water (usually hard water) contains metallic ions such as Ca.sup.2+, Mg.sup.2+, Fe.sup.2+ and the like, so that when the water is used for washing and deposited on the surfaces such as of products, these ions cause corrosion. Where products or parts are washed with detergents containing rust preventives, these products or parts have to be rinsed with clean water again. This requires additional costs for the rust preventives and an additional rinsing step.
Under these circumstances in the art, the invention has for its object the provision of washing water which is able to remove stains or contaminants such as of oils without use of any detergent and also method and apparatus for making the washing water at low costs by a simple manner.
Another object of the invention is to provide a method for immediately separating emulsified water obtained by removing oily substances with surface active agent-free water into oil phase and oil-free water phase.